Regarding the caster mercenaries, the dev team has been looking into it
since the initial reports on test but since none of the changes that
were pushed to test/live from beta are directly related to the mercenary
systems it's proven to be a bit of a mystery.
Regardless, we'll be poking at all the things until its fixed.

(Professor's voice) Good news, everyone!
We've tracked down the cause of the mercenary weirdness and are working on the fix now.

A temporary workaround until we patch out a fix is to re-sort the stance
list by clicking the blue 'Stance' text at the top of the Manage
Mercenary window and then selecting the stance you want the mercenary to
take.

Essentially the bug is causing the first option in the stance list to
put the mercenary into 'Passive' mode regardless of what stance is
listed first.

Thank you to all the players who reported the issue and mentioning that
re-ordering the stances fixed it for you, that helped immensely in
tracking this one down.